duality.ps.ps

国外开发的著名分布式操作系统mach的有关代码文章

(around which secondary storage management is structured.  It is the)
SH( Mach memory object abstraction)1 W
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(that most sets it apart from Accent)
106 W( and that gives Mach the ability to efficiently manage system services such as)105 W
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(network paging and filesystem support outside the kernel.)SH
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(3)SH
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(3.1. Execution Control Primitives)SH
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(Program execution in Mach is controlled through the use)
14 W( of tasks and threads.  A)15 W
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(task)SH
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(is the basic unit of resource)15 W
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(allocation. It)
264 W( includes a paged virtual address space and)
7 W( protected access to system resources such as processors and)6 W
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(communication capabilities.  The)160 W
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(thread)SH
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(is the basic unit of computation.  It is a lightweight process operating)160 W
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(within a)
129 W( task; its only physical attribute is its processing state \050)128 W
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(e.g.)SH
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(, program counter and registers\051.  All threads)128 W
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(within a task share the address space and capabilities of that task.)SH
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(3.2. Inter-Process Communication)SH
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(Inter-process communication \050IPC\051 in)
34 W( Mach is defined in terms of)35 W
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(ports)SH
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(and)SH
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(messages)SH
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(. These)
320 W( constructs provide)35 W
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(for location independence, security and data type tagging.)SH
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(A)SH
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(port)SH
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(is a)
150 W( communication channel.  Logically, a port is a finite length queue for messages protected by the)149 W
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(kernel. Access)
450 W( to a port is granted by receiving a message containing a port capability)
100 W( \050to either send or receive)101 W
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(messages\051. A)
250 W( port may have any number of senders but only one receiver.)SH
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(A)SH
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(message)SH
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(consists of a fixed length header and a variable-size collection of typed data objects.  Messages may)65 W
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(contain port capabilities or imbedded pointers as long as they are properly typed.  A single message may transfer)
22 W( up)23 W
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(to the entire address space of a task.)SH
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(msg_send\050message, option, timeout\051)SH
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(Send a message to the destination specified in the message header.)SH
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(msg_receive\050message, option, timeout\051)SH
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(Receive a message from the port specified in the message header, or the default group of ports.)SH
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(msg_rpc\050message, option, rcv_size, send_timeout, receive_timeout\051)SH
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(Send a message, then receive a reply.)SH
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(Table 3-1:)SH
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(Primitive Message Operations)SH
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(The fundamental primitive operations on ports are those to send and receive messages.)
2 W( These)
253 W( primitives are listed)1 W
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(Table 3-1.)
60 W( Other)
371 W( than these primitives and a few functions that return the identity of the calling task or thread,)61 W
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(all)SH
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(Mach facilities are expressed in terms of remote procedure calls on ports.)SH
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(The Mach kernel can itself be considered a task with multiple threads of control.)
31 W( The)
311 W( kernel task acts as a server)30 W
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(which in turn implements tasks and threads.  The act of creating)
35 W( a task or thread returns send access rights to a port)36 W
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(that represents the new task or thread)
60 W( and that can be used to manipulate it.  Messages sent to such a port result in)59 W
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(operations being performed on the object it represents.  Ports used in this way can)
9 W( be thought of as though they were)10 W
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(capabilities to objects in an object-oriented system)
148 W( [10].)
SH( The act of sending a message \050and)
148 W( perhaps receiving a)147 W
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(reply\051 corresponds to a cross-domain procedure call in a capability-based system such as Hydra [23] or StarOS [11].)SH
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(The indirection provided by message passing allows objects to be arbitrarily placed in the)
19 W( network without regard)20 W
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(to programming details.  For example, a thread can suspend another thread by sending a suspend message to the)
6 W( port)5 W
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(representing that other thread)
32 W( even if the request is initiated on another node in a network.  It is thus possible to run)33 W
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(varying system configurations on different classes of machines while providing a consistent)
288 W( interface to all)287 W
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(resources. The)
250 W( actual system running on any particular machine is more a function of its servers than its kernel.)SH
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(4)SH
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(Tasks allocate ports to represent their)
58 W( own objects or to perform communication.  A task may also deallocate its)59 W
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(rights to a port.  When the receive rights to a port are destroyed,)
32 W( that port is destroyed and tasks holding send rights)31 W
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(are notified.  Table 3-2 summarizes the operations available to manage port rights and control message reception.)SH
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(port_allocate\050task, port\051)SH
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(Allocate a new port.)SH
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(port_deallocate\050task, port\051)SH
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(Deallocate the task's rights to this port.)SH
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(port_enable\050task, port\051)SH
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(Add this port to the task's default group of ports for msg_receive.)SH
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(port_disable\050task, port\051)SH
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(Remove this port from the task's default group of ports for msg_receive.)SH
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(port_messages\050task, ports, ports_count\051)SH
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(Return an array of enabled ports on which messages are currently queued.)SH
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(port_status\050task, port, unrestricted, num_msgs, backlog, receiver, owner\051)SH
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(Return status information about this port.)SH
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(port_set_backlog\050task, port, backlog\051)SH
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(Limit the number of messages that can be waiting on this port.)SH
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(Table 3-2:)SH
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(Port Operations)SH
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(3.3. Virtual Memory Management)SH
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(A task's address space consists)
86 W( of an ordered collection of valid memory regions.  Tasks may allocate memory)87 W
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(2)SH
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(regions anywhere within)
219 W( the virtual address space defined by the underlying hardware)220 W
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(. The)
690 W( only restriction)220 W
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(imposed by Mach is that regions must be aligned on system page boundaries.  The system page size)
57 W( is a boot time)56 W
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(parameter and can be any multiple of the hardware page size.)SH
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(Mach supports read/write sharing of memory among tasks of)
146 W( common ancestry through inheritance.  When a)147 W
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(child task is created, its address space may share \050read/write\051 or copy)
14 W( any region of its parent's address space.  As in)13 W
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(Accent, copy-on-write sharing is used to efficiently perform virtual memory copying both)
61 W( during task creation and)62 W
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(during message transfer.)SH
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(Table 3-3 summarizes the full set of virtual memory operations that can be performed on a task.)SH
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(3.4. External Memory Management)SH
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(An important part of the Mach strategy)
96 W( was a reworking of the basic concept of secondary storage.  Instead of)95 W
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(basing secondary storage around a kernel-supplied file system \050as)
163 W( was done in Accent and Aegis\051, Mach treats)164 W
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(secondary storage objects in the same way as other server-provided resources accessible through)
72 W( message passing.)71 W
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(This form of)112 W
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(external memory management)113 W
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(allows the advantages of a single level store to be made available to)113 W
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(ordinary user-state servers.)SH
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(The Mach external memory management interface is based on the)
58 W( the Mach)57 W
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(memory object)57 W
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(. Like)
364 W( other abstract)57 W
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(objects in the Mach environment, a memory object is represented by a)
7 W( port.  Unlike other Mach objects, the memory)8 W
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(2)SH
8 SS 
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(For example, an RT PC task can address)
17 W( a full 4 gigabytes of memory under Mach while a VAX task is limited to at most 2 gigabytes of user)16 W
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(address space by the hardware.)SH
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(5)SH
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(vm_allocate\050task, address, size, anywhere\051)SH
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(Allocate new virtual memory at the specified address or anywhere space can be found \050filled-zero on demand\051.)SH
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(vm_deallocate\050task, address, size\051)SH
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(Deallocate a range of addresses, making them no longer valid.)SH
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(vm_inherit\050task, address, size, inheritance\051)SH
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(Specify how this range should be inherited in child tasks.)SH
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(vm_protect\050task, address, size, set_max, protection\051)SH
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(Set the protection attribute of this address range.)SH
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(vm_read\050task, address, size, data, data_count\051)SH
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(Read the contents of this task's address space.)SH
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(vm_write\050task, address, count, data, data_count\051)SH
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(Write the contents of this task's address space.)SH
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(vm_copy\050task, src_addr, count, dst_addr\051)SH
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(Copy a range of memory from one address to another.)SH
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(vm_regions\050task, address, size, elements, elements_count\051)SH
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(Return a description of this task's address space.)SH
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(vm_statistics\050task, vm_stats\051)SH
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(Return statistics about this task's use of virtual memory.)SH
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(Table 3-3:)SH
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(Virtual Memory Operations)SH
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(object is not provided solely by the Mach kernel, but can be created and serviced by a user-level data manager task.)SH
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(A memory object is an abstract object representing a collection of data bytes on which)
87 W( several operations \050)86 W
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(e.g.)SH
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(,)SH
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(read, write\051 are defined.  The data manager is entirely responsible for the initial values of)
231 W( this data and the)232 W
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(permanent storage of the data)
180 W( if necessary.  The Mach kernel makes no assumptions about the purpose of the)179 W
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(memory object.)SH
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(In order to make memory object data)
14 W( available to tasks in the form of physical memory, the Mach kernel acts as a)15 W
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(cache manager for the contents of the memory object.  When a page fault)
134 W( occurs for which the kernel does not)133 W
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(currently have a valid cached resident page, a remote procedure call is made on the memory object requesting)
62 W( that)63 W
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(data. When)
346 W( the cache is full \050)48 W
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(i.e.)SH
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(, all physical)
48 W( pages contain other valid data\051, the kernel must choose some cached)47 W
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(page to replace.  If the data in that page was modified while it)
59 W( was in physical memory, that data must be flushed;)60 W
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(again, a remote procedure call is made on the memory object.  Similarly, when all references)
31 W( to a memory object in)30 W
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(all task address maps are relinquished, the kernel releases the cached pages for)
114 W( that object for use by other data,)115 W
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(cleaning them as necessary.)SH
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(For historical reasons, the external memory)
38 W( management interface has been expressed in terms of kernel activity,)37 W
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(namely paging.  As a result, the term)37 W
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(paging object)37 W
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(is often used)
37 W( to refer to a memory object, and the term)38 W
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(pager)SH
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(is)SH
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(frequently used to describe the data manager task that implements a memory object.)SH
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(3.4.1. Detailed Description)SH
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(The interface between data manager tasks and the Mach kernel consists of three parts:)SH
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(\267)SH
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(Calls made by an application program to cause a memory object to)
87 W( be mapped into its address space.)86 W
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(Table 3-4 shows this extension to Table 3-3.)SH
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